Customizing Using Dynamic Properties

There are many situations where we need to present a form that has mandatory fields. To indicate to the user that the field is mandatory, one effective (albeit esthetically dubious) solution is to use yellow as the background color for those fields. It turns out this is very easy to implement using Qt Style Sheets. First, we would use the following application-wide style sheet:

*[mandatoryField="true"] { background-color: yellow }

This means that every widget whose mandatoryField Qt property is set to true would have a yellow background.

Then, for each mandatory field widget, we would simply create a mandatoryField property on the fly and set it to true. For example:

Things look already a lot better. But the button looks a bit cramped. Let's specify some spacing between the border and the text using the padding. Additionally, we will enforce a minimum width, round the corners, and specify a larger font to make the button look nicer:

Customizing the QPushButton's Menu Indicator Sub-Control

Subcontrols give access to the sub-elements of a widget. For example, a QPushButton associated with a menu (using QPushButton::setMenu()) has a menu indicator. Let's customize the menu indicator for the red push button:

By default, the menu indicator is located at the bottom-right corner of the padding rectangle. We can change this by specifying subcontrol-position and subcontrol-origin to anchor the indicator differently. We can also use top and left to move the indicator by a few pixels. For example:

Customizing QProgressBar

The QProgressBar's border, chunk, and text-align can be customized using style sheets. However, if one property or sub-control is customized, all the other properties or sub-controls must be customized as well.

Customizing QScrollBar

The QScrollBar can be styled using its subcontrols like handle, add-line, sub-line, and so on. Note that if one property or sub-control is customized, all the other properties or sub-controls must be customized as well.

The scroll bar above has been styled in aquamarine with a solid grey border.

Common Mistakes

This section lists some common mistakes when using stylesheets.

QPushButton and images

When styling a QPushButton, it is often desirable to use an image as the button graphic. It is common to try the background-image property, but this has a number of drawbacks: For instance, the background will often appear hidden behind the button decoration, because it is not considered a background. In addition, if the button is resized, the entire background will be stretched or tiled, which does not always look good.

It is better to use the border-image property, as it will always display the image, regardless of the background (you can combine it with a background if it has alpha values in it), and it has special settings to deal with button resizing.

The numbers after the url gives the top, right, bottom and left number of pixels, respectively. These numbers correspond to the border and should not stretch when the size changes. Whenever you resize the button, the middle part of the image will stretch in both directions, while the pixels specified in the stylesheet will not. This makes the borders of the button look more natural, like this: